Meeting Abstract
102.7 Tuesday, Jan. 7 09:30 Thermoregulation and energetics in hibernating black bears: The mystery of multi-day body temperature cycles. BARNES, BM*; TOIEN, O; Univ of Alaska Fairbanks bmbarnes@alaska.edu
Black bears overwintering in outdoor hibernacula in Fairbanks, Alaska don’t move much, reduce whole body metabolism to as low as 25% of basal rates, and decrease core body temperature (Tb) from summer levels of 37-38 °C to a hibernation season average of 33 °C. Tb is not stable during hibernation, however, but instead displays cycles of 2-7 days in length and amplitudes reaching 6 °C. The cause of and reason for these unusual Tb cycles are not known, although we do not believe they are homologous to spontaneous arousals in small mammalian hibernators. To investigate the dependency of Tb cycles on thermoregulatory conditions, we kept 12 hibernating bears with body mass from 35.5-116.5 kg in undisturbed outdoor enclosures and manipulated den temperature (Tden) while recording bear Tb, metabolic rate, shivering, and movement. Bears shivered to produce heat preventing Tb from decreasing below 30 °C. Tb cycles shortened as Tden decreased (mean R2= 0.70), suggesting that cooling rate determines period length, however large bears with lower thermal conductance had the same or shorter Tb cycle length than small bears. Metabolic rate averaged over complete Tb cycles was negatively correlated to Tden below lower critical temperatures, which varied among bears from 1.4°C to 10.4°C. We conclude that the patterns of Tb cycling in hibernating black bears is related to the demand for thermoregulatory heat production by shivering, but we can only speculate as to their functional significance.
